I don't see any images tagged with this, you sure this tag exists?
I can see how this would be something unique apart from Cum in Mouth where there's too much to keep in the mouth (or it's open) so it falls out.
I would oppose "gush" though because it has unclear meaning. Liquids can gush in or gush out, so it doesn't indicate direction.
Possibly "cum_overflow" could work.
I don't know if we should have separate ones for oral or anal/vaginal. Searching it in combination with in_mouth or in_vagina and so on could give those subsets without inventing names for them.